The objective of the Program on Surgical Control of the Hyperlipidemias (POSCH) is to prove, or disprove, the lipid-atherosclerosis hypothesis by maximal cholesterol reduction in an unifactorial secondary intervention trial of 1,000 subjects (500 control and 500 treated), in which data analysis includes objective and quantitative assessment of coronary atherosclerotic plaque lesions. Maximal cholesterol reduction is defined as the cholesterol lowering achieved by the partial ileal bypass operation. This procedure has been proven to be safe, lasting, and, of course, obligatory - i.e. having its lipid effects free from patient influence. The lipid derived from the POSCH trial itself, with both the control and operated groups on a cholesterol-lowering diet, have documented the total cholesterol concentration to be 37% lower in the partial ileal bypass group, accompanied by a 47% lower LDL-cholesterol level. Unifactorial trial is defined as a trial of lipid reduction with, as far as possible, freedom from confounding risk factors by exclusion. Secondary intervention is intervention in the atherosclerosis progress after that process has progressed to overt disease, as manifested by a single, well-documented myocardial infarction. The POSCH trial, in addition to the traditional assessment of clinical endpoints and events, and the evaluation of sequential graded stress electrocardiograms, will employ computerized reading and weighted numerical comparisons of sequential peripheral and coronary arteriograms. For a brief review of the history of the POSCH, the past achievements of this program, and the current policy position of the principal investigators, the reader is referred to the Executive Summary section of the narrative. We submit that in order to provide (possibly ever) a definitive answer to the lipid-atherosclerosis hypothesis for secondary intervention, this imperative trial must be adequately funded, until it is scientifically concluded (a current five-year grant is mandatory), and this trial must be allowed to immediately add one clinical center (Lankenau Hospital, Philadelphia, Pennsylvania), for a modest total of four.